Sha'anan Streett, the frontman of Hadag Nahash - the biggest hip-hop band in Israel - is hung over. And the waitress in the Jerusalem cafe clearly knows it. "Black coffee followed by a big green salad?" she suggests. He gives her a wry smile. "You know me too well," he replies.

Then he turns to me, sotto voce. "Last night," he murmurs, "too many substances." He motions to his "f*** the police" T-shirt. "This is my own design," he tells me.

It is all very hip-hop. But there is more to Sha'anan Streett than meets the eye. For one thing, he is a devoted family man, in a stable marriage with three small children. For another, he still lives in Jerusalem; all the other members of the band moved to the bright lights of Tel Aviv. And most strikingly of all, he is the brains behind the One Shekel Festival - so called because it only costs a shekel to attend - which takes place every year in the most disadvantaged areas of Israel.

From the very beginning, Streett has been a politically motivated musician. His first song, which he wrote after completing his army service, was a droll, laid-back acid-jazz tune called Shalom Salaam Peace.

"I couldn't play anything but the recorder," he says, "but I could rap. And I felt very strongly about politics. I made 300 copies of Shalom Salaam Peace, and went round selling it in CD shops."

One of the shop assistants was a musician, and they agreed to start a band. Hadag Nahash - which means "eel" in Hebrew, and puns on nahag hadash, or "new driver" - was born.

"It was amazing," recalls Streett, "Shalom Salaam Peace went straight to number one. It was like a dream come true."

Evidently there was an audience for peacenik hip hop. With lyrics like "a land that has peace is a land of fun/ and a land without peace is a land of foul mess," there could be no mistaking Streett's political orientation.

The musician's ideological stance was sharpened around 10 years ago by way of a much-publicised vendetta with the right-wing rapper Subliminal. Streett, munching his big green salad, has little time for his old rival. "Subliminal is a businessman, not a musician," he says. "He made big Zionist statements, but he was only aiming for sales."

His view is apparently confirmed by Subliminal's latest career move. His most recent song, At Me, a duet with Dana International (the Israeli transsexual winner of the 1998 Eurovision song contest), features the lyric "sexy, sexy, sexy, sexy boy".

Streett is not surprised. "It's only to be expected," he says, "Subliminal has seen another business opportunity. He's dropped his politics because it no longer suits him."

Hadag Nahash, meanwhile, have made no compromises. Their latest album, released this year, features songs in Hebrew and Arabic, and includes tracks like One More Brother, a protest against violence in Israeli society.

This is reflected in Streett's passion for the One Shekel Festival. Back in 2000, when Hadag Nahash were riding the first wave of fame, his immediate instinct was to help the poorer communities in Israel.

"That summer we played at the music festivals," Streett recalls, "to audiences that were 10 times the size of what we were used to. I got off stage really fired up. In the toilet I saw two kids who were panicking. The festival was in Ashkelon, on the beach, and they couldn't afford to get in - so they had swum around the barrier, and were terrified of getting caught."

Then and there, Streett decided to do something. "I entered the bathroom Superman, and came out Clark Kent," he tells me. "I realised that unlike myself, many people in the country didn't have the money to go to gigs. That's how the idea of the One Shekel Festival started."

Since then, it has gone from strength to strength, attracting thousands of people from disadvantaged areas each year. Moreover, Streett has used the events to foster Jewish-Arab relations.

"It's great to have Jewish and Arab bands performing together," he says, "but it's not always easy. Last year an Arab band made inflammatory comments about martyrs in Gaza. The festival was almost closed down. But when you see Muslim girls in headscarves wearing a One Shekel Festival T-shirt, with our slogan, 'culture is a basic right', it makes it all worth it."